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Old 06-18-2011, 01:52 PM
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Vega horsepower vs torque questions.

My street Vega has a SBC 427 9.88:1 compression stroker motor, TH400 w/3000 stall converter and a 12 bolt w/3:73 posi.

A chassis dyno was performed and the results were both disappointing and impressive. Seven runs were done. At 5500 RPM's, the engine HP is 357 and the torque is 549. I'm good with the monster torque but I was expecting at least one HP per cubic inch. Two of the runs are on You Tube under '72 Chevrolet Vega dyno run.

On the engine build, I opted to re-use the Edelbrock "Performer RPM" 64cc heads and the dual plane "Performer RPM/Air Gap" intake from the old motor; both are ported and polished. How much HP did I give up by not using better flowing heads? How much by not using for example a single plane intake?
Are those dyno #'s respectable considering the car? My intentions are for street use; I don't have any plans to race it.

Thanks in advance for your replies.

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Old 06-18-2011, 02:14 PM
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you talkin to me?
 
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What cam? If you have a 3000 stall and a dual plane that alone is a problem
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Old 06-18-2011, 02:18 PM
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The torque is 549 ft lbs at 5500 rpm? What are the specs on the cam?
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Old 06-18-2011, 02:40 PM
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He must mean peak torque. At 5500 rpm, 549 ft-lbs would be 575 hp.
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Old 06-18-2011, 02:43 PM
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Comp "Magnum" H/Roller P/N 12-450-8, 560 lift / 286 duration, 108 lobe center angle.
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Old 06-18-2011, 03:01 PM
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You will never get a impressive horsepower figure from a chassis dyno.

Take your car to the drags and run it in the time trials.

The MPH is directly related to the Real net (installed) engine horsepower/weight.
It never lies. Chassis dynos are subject to all kinds of errors.
(Tires, tire pressure, converter stall effect, calibration etc.)

If all you wanted from the chassis dyno session was a horsepower figure (for bragging rights or what ever), you wasted your time and money.

Use a chassis dyno only as a tuning tool. Not for finding out how much HP you got (or want). It doesn't do that.

If you never intend to race the car, what difference does it make?

Last edited by F-BIRD'88; 06-18-2011 at 03:13 PM.
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Old 06-18-2011, 03:06 PM
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Does the engine only spin to 5500 rpm? What hp did it make above 5500?
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Old 06-18-2011, 03:40 PM
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Quote:
Originally Posted by nofearengineer
He must mean peak torque. At 5500 rpm, 549 ft-lbs would be 575 hp.
Forgive my ignorance, how did you come up with that calculation?

Chassis dynos measure HP at the rear wheels so I guess the system calculates an estimated engine HP. You and I are both questioning the HP #'s based on the torque #'s. The dyno guy re-verified the HP #'s several times. Estimated HP #'s from the engine builder was 465+/- so something is funky.

I just can't help but wonder if that 357 HP is actually RWHP, not engine HP.
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Old 06-18-2011, 03:59 PM
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Quote:
Originally Posted by F-BIRD'88
You will never get a impressive horsepower figure from a chassis dyno.

Take your car to the drags and run it in the time trials.

The MPH is directly related to the Real net (installed) engine horsepower/weight.
It never lies. Chassis dynos are subject to all kinds of errors.
(Tires, tire pressure, converter stall effect, calibration etc.)

If all you wanted from the chassis dyno session was a horsepower figure (for bragging rights or what ever), you wasted your time and money.

Use a chassis dyno only as a tuning tool. Not for finding out how much HP you got (or want). It doesn't do that.

If you never intend to race the car, what difference does it make?
Points well taken. I did the chassis dyno as a dyno tune but I was shocked by the low HP #. It was expected to be 465+/-.
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Old 06-18-2011, 04:02 PM
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Yes a chassis dyno measures hp at the rear wheels and gives you the power at the rear wheels. If the builder told you 465 engine hp then he's probably not all that far off.

Horsepower equals torque x rpm/5252 so 575hp equals 549lb ft x 5500 rpm /5252.

Horsepower is a calculated figure based on torque and RPM. Above 5252 rpm horsepower is always greater than torque and below 5252 rpm torque is always greater than horsepower. That is on any engine, anywhere in the world.

Last edited by Blazin72; 06-18-2011 at 04:10 PM.
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Old 06-18-2011, 04:03 PM
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1.21 giga-watts???!!!!
 
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First of all, the valvetrain on a big block is extremely heavy, not conducive to high HP. Secondly, and most importantly, that must have been rear wheel HP.

What's the problem aside from not having something to brag about while bench racing? You have made an absolute killer street engine and I seriously doubt you'll be able to make it hook up. Most of that power will go up in smoke anyways. Either that or you will be breaking driveline parts regularly.
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Old 06-18-2011, 04:16 PM
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Quote:
Originally Posted by Blazin72
Does the engine only spin to 5500 rpm? What hp did it make above 5500?
Motor wasn't taken above 5500 rpm's; new motor.
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Old 06-18-2011, 04:17 PM
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You got a leaky spark tube...
 
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It may make more power if you rev it higher
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Old 06-18-2011, 04:20 PM
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CRD, he has a SBC, not a BBC.
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Old 06-18-2011, 04:36 PM
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Quote:
Originally Posted by cool rockin daddy
First of all, the valvetrain on a big block is extremely heavy, not conducive to high HP. Secondly, and most importantly, that must have been rear wheel HP.

What's the problem aside from not having something to brag about while bench racing? You have made an absolute killer street engine and I seriously doubt you'll be able to make it hook up. Most of that power will go up in smoke anyways. Either that or you will be breaking driveline parts regularly.
The motor is a small block, not a big block, but I see your points.
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